Manhole ladders which are permanently fixed to the inside wall of a manhole are typically wholly located within the manhole below its upper rim so that the manhole entrance can be covered with a manhole plate or grate. The fact that the ladder does not extend above the manhole entrance makes it difficult to mount and dismount the top end of the ladder. Therefore, manhole users must support and balance themselves from the rim of the manhole during entry until their bodies are almost entirely within the manhole and their hand can grasp the top rung of the manhole ladder, and likewise upon exiting the manhole. Such entry and exit is dangerous since users can slip and fall during these maneuvers, causing injury. The danger and inconvenience is augmented when users must carry tools, building materials or the like into and out of the manhole.
Some prior art devices have been proposed to address this problem, although with limited success. In particular, U.S. Pat. Nos. 3,598,200 (Thompson) and 4,546,855 (Lyons) both disclose a single rod device extendible from inside a manhole where it is slidably attached to the middle of the upper rungs of a manhole ladder. Thompson has a support at the lower end of the rod to releasably engage a ladder rung to retain the rod in an extended position. The support may be accidentally dislodged during use by a relatively small upward movement of the rod, causing the rod to collapse. The Lyons rod has an involved arrangement of brackets, plates and pins which must be hand-activated by a lever mechanism to retain the rod in an extended position. The arrangement is cumbersome since it requires a two-handed operation to raise and lower the rod. The number of parts in the Lyons system makes it needlessly complex and expensive to produce. In any event, the rods of both patents obstruct the middle of each manhole ladder and consume what little space one has on the rungs of the ladder for foot and hand placement. The location of the rods also requires a user to swing about the post in order to mount and dismount the ladder, which is a potentially dangerous maneuver over an open manhole. There is also the inconvenience of not being able to carry tools or the like since both hands must grasp the post during such maneuvering.
What is therefore desired is a novel device to facilitate safe entry and exit of a manhole on a manhole ladder and which overcomes the limitations and disadvantages of the prior art devices. Preferably, the device should provide two retractable safety posts that do not interfere with foot space on any ladder rungs, that are located on the sides of the ladder to allow direct access to the ladder rungs while providing a user with hand support, and that provide a user with the option of support with one or both hands, particularly when carrying tools or the like. The posts should be capable of quick and convenient extension and retraction with a simple means of positively locking the posts when extended. The device should further be inexpensive to manufacture and install, and be reliable and safe to use.